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If you’ve ever dealt with diarrhea, you know how quickly it leaves you feeling depleted. Now imagine a case that rages on and on — or comes back again and again.

This is the reality for nearly 500,000 Americans each year who have the bacterial infection known as Clostridioides difficile, or C. diff. Virulent diarrhea and inflammation of the colon can even turn life-threatening.

This primer will help you understand how C. diff spreads and releases toxins, what the common symptoms are, and who is most vulnerable. Dr. Jessica Allegretti, director of the fecal microbiota program at Harvard-affiliated Brigham and Women’s Hospital, also touches on promising preventive strategies and treatments.

How does C. diff spread?

Like many bacteria, C. diff is present in our stool. It’s carried by virtually everyone — on our skin and even on the soles of our shoes. When C. diff bacteria are outside the body, they are inactive spores. They only have a chance to become active when they’re swallowed and reach the intestines.

Even then, many people who swallow C. diff spores never become ill. The spores only sicken people whose gut microbiome — the trillions of organisms living in their intestines — becomes imbalanced for one of the various reasons described below. When an imbalance occurs, the spores start to multiply and create toxins that lead to a C. diff infection.

“Many of us are colonized with C. diff bacteria without any consequences,” says Dr. Allegretti. “We’re swallowing C. diff spores all the time. Only under the right circumstances will the spores germinate and release a toxin. It’s the toxin that makes you sick.”

What are the symptoms of a C. diff infection?

The symptoms mimic those of many other types of gastrointestinal ailments. Initially, this may make it difficult to tell the infection apart from milder illnesses.

Symptoms to watch for include

• persistent diarrhea lasting three or more days
• nausea
• fever
• stomach pain or tenderness
• appetite loss.

“C. diff isn’t something that people in the general population should be walking around scared of,” Dr. Allegretti says. “But if you need to take an antibiotic, be on the lookout for diarrheal symptoms after finishing the course of antibiotics. Diarrhea that’s associated with antibiotics alone should resolve once you finish taking the medication.”

Who is most vulnerable?

A few sobering facts from the Centers for Disease Control (CDC):

• C. diff is the top cause of health care-associated infections in the US.
• It disproportionately strikes people in hospitals and nursing homes.
• Among people over 65, one in 11 of those diagnosed with a health care-associated case of C. diff dies within a month.

However, other groups are also susceptible to the infection. Health care-associated C. diff infections are plateauing, Dr. Allegretti notes, while so-called community-based infections that occur among the general population are increasing.

People most likely to experience such infections:

• Are taking antibiotics or have just finished a course of antibiotic therapy. People are up to 10 times more likely to get C. diff while on antibiotics or during the month afterward, according to the CDC. “Not everyone who takes an antibiotic gets C. diff, and not everyone who gets C. diff gets recurrent C. diff,” says Dr. Allegretti. “It has a lot to do with your host response, your gut microbiome, and your individual risk factors, such as immunosuppression or inflammatory bowel disease.”
• Have a weakened immune system due to cancer, organ transplant, or treatment with immunosuppressive drugs (such as people with inflammatory bowel disease or autoimmune conditions).
• Have close contact with someone who has been diagnosed with C. diff.

What prevention strategies help block the spread of C. diff?

Hospitals try to prevent C diff. among patients in several ways. They impose scrupulous hand-washing requirements among staff members. Patients who develop new diarrhea are tested for C. diff infection. Those who have it are isolated in their own rooms to help prevent further spread.

Outside of a hospital, you can help prevent this gut infection through a few commonsense measures.

• Wash your hands thoroughly with soap and water every time you use the bathroom and always before eating. Clean hands are especially important if you’ve had C. diff or know you’ve been exposed to someone with it. By the way, alcohol-based hand sanitizer isn’t effective against C. diff because its organisms can form resistant spores.
• Take antibiotics only when strictly necessary and for the shortest period possible. “The biggest thing we can do is advocate for ourselves,” Dr. Allegretti says. “During cold and flu season, we know a lot of unnecessary antibiotic prescriptions are written for infections that are most likely viral, not bacterial. Antibiotics do not kill viruses — and unnecessary antibiotics may upset the bacterial balance in your gut. Ask your doctor: Do I need this prescription? Is there an alternative?”
• When you do need antibiotics, ask if a narrow-spectrum antibiotic would be effective for your type of infection. Why? Broad-spectrum antibiotics kill a wider array of bacteria. This may be overkill, depleting your gut microbiome unnecessarily and enabling C. diff bacteria to germinate. “The caveat is, we don’t want patients to not take antibiotics they need for an actual infection,” she says. “But have a conversation with your health care team.”

The type of antibiotic prescribed also matters, according to a 2023 study in the journal Open Forum Infectious Diseases. Researchers compared more than 159,000 people who had C. diff infection with 797,000 healthy controls. Study findings suggest that using clindamycin and later-generation cephalosporin antibiotics pose the greatest risk for C. diff infection. Meanwhile, the antibiotics minocycline and doxycycline were associated with the lowest risk.

“But there are very few safe antibiotics with regard to C. diff risk,” Dr. Allegretti says.

Can probiotics help prevent or treat C. diff infection?

Probiotics are live microorganisms that can help keep the gut healthy and are found in supplements, yogurt, and other fermented foods. Two familiar examples are various strains of Lactobacillus and Bifidobacterium.

However, probiotics haven’t been found to prevent C. diff or its recurrence. Research performed in mice and humans suggests that giving probiotics after a course of antibiotics may slow the pace of microbiome recovery. “You’re potentially delaying the recovery of your microbiome with probiotics,” she says.

How is C. diff infection treated?

Ironically, C. diff therapy typically starts with antibiotics, despite the infection’s proliferation due to antibiotic use. The antibiotics of choice include fidaxomicin or oral vancomycin.

However, about one in five people will suffer one or more recurrences –– and with each one, yet another recurrence becomes far likelier, Dr. Allegretti says. A repeat episode may happen because people haven’t disinfected their homes effectively. That leaves them open to reinfection with the same strain of C. diff while still vulnerable.

When C. diff recurs, fecal microbial transplants (FMT) are considered the gold standard treatment. FMT transplants fecal matter from a healthy donor into a patient’s gut, placing it there using an endoscope, enema, or within an oral capsule. This year, the FDA approved two live fecal microbiota products aimed at preventing recurrent C. diff infections.

“We haven’t gotten away from antibiotics yet to treat this disease,” says Dr. Allegretti. “But we have a lot of preventative strategies now. It’s certainly very exciting for people struggling with C. diff infections.”

About the Author

Maureen Salamon, Executive Editor, Harvard Women's Health Watch

Maureen Salamon is executive editor of Harvard Women’s Health Watch. She began her career as a newspaper reporter and later covered health and medicine for a wide variety of websites, magazines, and hospitals. Her work has … See Full Bio View all posts by Maureen Salamon

About the Reviewer

Howard E. LeWine, MD, Chief Medical Editor, Harvard Health Publishing

Dr. Howard LeWine is a practicing internist at Brigham and Women’s Hospital in Boston, Chief Medical Editor at Harvard Health Publishing, and editor in chief of Harvard Men’s Health Watch. See Full Bio View all posts by Howard E. LeWine, MD

Birth control pills have been safely used in the US (and sold only by prescription) for more than half a century. Just this past summer, the FDA approved Opill, the first daily contraceptive pill intended for sale over the counter. This offers many more people access to a new nonprescription option for preventing pregnancy.

Opill may be available early in 2024, although the exact date and cost are not yet known. Here’s what anyone interested — adults, parents, and teens — should know.

What is in Opill and how does it work?

Opill is a progestin-only form of birth control. That means it uses a single hormone called progestin (or norgestrel) to prevent pregnancy. It works by

• affecting ovulation so that the ovaries do not release an egg every month
• thickening cervical mucus, which blocks sperm from reaching an egg
• changing the uterine lining in ways that keep a fertilized egg from implanting.

How effective is Opill at preventing pregnancy?

It depends on how consistent you are about taking Opill:

• Perfect use means taking the pill every single day at the same time. With perfect use, Opill is 98% effective. That means that if 100 people take the medication perfectly, two or fewer people would become pregnant. Taking a pill perfectly can be difficult, though.
• Typical use averages how well a method works to prevent pregnancy when real people use it in real life. It considers that people sometimes use the pill inconsistently, like forgetting a dose or not taking it at the same time every day. With typical use, Opill is 91% effective. This means that if 100 people use Opill, but don’t take it perfectly, at least nine could become pregnant in a year.

It's also important to know that some medications make Opill less effective at preventing pregnancy. These include medicines used to treat migraines and seizures. Even though this birth control pill will be available over the counter, you should ask your health care provider if any medicines you take could make it less effective.

How do you take Opill?

• Take it once a day at the same time each day until you finish the entire pack.
• Sticking to a consistent time of day, every day, is crucial. Timing matters with progestin-only pills like Opill because this medication works by raising progestin levels. However, progestin only stays elevated for 24 hours after you take each pill. After that, the progestin level will return to normal.
• After you complete a 28-day pack, you should immediately start a new pack of pills the next day.

What happens if you forget to take a dose at the specific time or miss a dose?

• If you take the pill more than three hours late it will not be as effective at preventing pregnancy.
• Take the missed pill as soon you remember.
• You will need to use a backup birth control method such as condoms every time you have sex for the next 48 hours.

Is Opill safe for teenagers?

Opill is generally safe for most people who could get pregnant, including teenagers. There’s no evidence to suggest that safety or side effects are different in teenagers compared with adults.

Research done by the manufacturer has established the safety of Opill in people as young as 15 years old. It will be available without an age restriction.

When teens use birth control, what is the best choice for them?

There isn't a one-size-fits-all birth control method for all teenagers. The best method is the one a teen personally prefers and is committed to using consistently.

For teens who struggle with taking medication at the same time every day –– or anyone else who does –– Opill may not be the right choice. Fortunately, there are many options for preventing pregnancy, catering to individual preferences and goals.

Learn more about different contraception methods at the Center for Young Women’s Health website.

What side effects are common with Opill?

Progestin-only pills are usually associated with mild side effects. The most common side effects are:

• unexpected vaginal bleeding or spotting
• acne
• headache
• gastrointestinal symptoms such as nausea, abdominal pain, and bloating
• change in appetite.

Opill does not cause problems with getting pregnant in the future, or cause cancer. Unlike birth control pills that combine the hormones estrogen and progestin, Opill will not increase the risk of a developing a blood clot.

Will Opill cause any mood changes?

Research looking at possible effects of progestin-only pills on mood is limited, so this is unclear. We do know that most people who take hormonal birth control methods do not experience negative mood changes.

Fortunately, there are many different types of effective birth control. If one method causes you unwanted side effects, talk to your health care provider. Together, you can figure out if another type of birth control may work better for you.

Can it be used as emergency birth control?

No, it should not be used as emergency birth control.

What should you know about STIs?

This type of birth control does not protect you from sexually transmitted infections (STIs) such as syphilis, gonorrhea, or chlamydia.

You can reduce the chance of getting STIs by correctly using condoms each time you have sex. There are different types of condoms: one made for penises and one made for vaginas.

Vaccines help protect against some STIs such as hepatitis B and human papillomavirus (HPV). A medicine called PrEP can help prevent HIV. Ask your medical team for more information about the right choices for you.

When will Opill be available and what will it cost?

The timeline for availability and the cost of medication is determined by the manufacturer. At time of FDA approval, it was expected to hit shelves in early 2024. No updates have been released for the exact date or estimated cost of the medication.

About the Authors

Candice Mazon, MD, Contributor

Dr. Candice Mazon is a second year adolescent medicine fellow at Boston Children's Hospital. She's a board certified pediatrician and received her training at MedStar Georgetown University Hospital. She earned her MD degree from Drexel University … See Full Bio View all posts by Candice Mazon, MD

Amy Desrochers DiVasta, MD, MMSc, Contributor

Amy Desrochers DiVasta MD, MMSc, is chief of the division of adolescent medicine at Boston Children’s Hospital. She is the co-director of the adolescent long-acting reversible contraception program, and co-director of the reproductive endocrinology and PCOS … See Full Bio View all posts by Amy Desrochers DiVasta, MD, MMSc